1. Field of the Invention
The present invention relates to a method of producing file management structures different from each other in an information recording medium, and an apparatus and method for reproducing information from the information recording medium.
2. Description of Prior Art
Digital data are recorded in a form of a file in a recording medium in an external memory device such as a magnetic disk device or an optical disk device.
The data recorded in a recording medium are read by an apparatus such as a computer, and such an apparatus uses an operating system having its own file management system.
As mentioned above, each operating system has a different file management system for managing files efficiently. Therefore, if a file for data is allocated in an information recording medium with use of an operating system, the data cannot be read from the information recording medium with use of a different operating system.
For example, FIG. 1 shows a diagram of areas in an information recording medium in the file space system of UNIX which is a well known operating system for work stations. In FIG. 1, numeral 101 designates a boot area for recording a boot program for starting a system, numeral 102 designates a super block area for recording management information on the entire file system such as the size of the area of the file system and the size and the position of free areas not used for recording, numeral 103 designates an area for recording an inode list which is a collection of the information on files and directories such as the positions and the sizes thereof, and numeral 104 designates a data area for recording the data of the files and directories. In this file space system, file management information on the root directory and subdirectories is also recorded in the data area 104.
FIG. 2 displays a diagram for explaining an operation to reproduce a data file F1 registered in the root directory. First, the inode 130 of the root directory is read from the inode list area 103. The inode is managed with inumbers, and an inode of inumber "2" corresponds with the inode 130 of the root directory. In the inode 130, the size and the block address of the root directory are described. In UNIX, areas are managed by dividing them into blocks each consisting of a plurality of successive sectors. The root directory data 140 which are recorded in blocks represented by the block addresses is read in the data area 104 according to the block address. In the root directory data 140, file names and inumbers of the inode of files are described, and an inode 131 having the inumber of the file F1 is read. Then, the size of file F1 and the blocks wherein the data of the file F1 are recorded are obtained, and the data 141 of the file F1 is read in the data area 104 according to the inode 131 of file F1. When the data of a file is recorded in a plurality of blocks, the inode manages all blocks.
FIG. 3 shows a file space system in a recording medium 200 of MS-DOS which is a well known operating system for personal computers. In FIG. 3, numeral 201 designates a boot area for recording a boot program for starting a system, numeral 202 designates an area for a file allocation table (FAT) for recording the use status of a recording medium such as the sizes and the positions of files and subdirectories, the position of free areas not used and the position of defective areas, numeral 203 designates an area for another FAT usually recorded in order to enhance reliability, numeral 204 designates a root directory area for recording a root directory, and numeral 205 designates a data area for recording the data of data files and subdirectories. In this data structure, file management information on subdirectories is recorded in the data area 205.
FIG. 4 displays a diagram for explaining an operation to reproduce a data file F2 registered in the root directory. First, the root directory data 240 are reproduced from the root directory area 204. The root directory describes names, top cluster numbers and sizes of files. In MS-DOS, areas are managed by being divided into clusters consisting of a plurality of successive sectors. The data 250 of the file F2 is reproduced from the cluster designated by the top cluster number in the data area 205. If the data of a file is recorded in a plurality of clusters, the cluster addresses of the second and following clusters are obtained by reproducing the FAT in the area 202.
Thus, the data structures of file management information of UNIX and of MS-DOS are different from each other. In UNIX, the data of files are managed by inodes and directories, while in MS-DOS, they are managed by directories and FAT. The contents of a directory are also different in the two operating systems. That is, in UNIX, file names and inumbers are recorded in a directory, while in MS-DOS, file names, file sizes and top cluster numbers are recorded in a directory.
As explained above, UNIX and MS-DOS have different file management systems. Therefore, even the same data of a file which are recorded with one of the operating systems cannot be reproduced with the other.